Selective deposition of semiconductor materials



J. F. WATSON 3,409,483

SELECTIVE DEPOSITION OF SEMICONDUCTOR MATERIALS Nov. 5, 1968 2 Sheets-Sheet 1 Original Filed May 1, 1964 II DQDLDDQQO /f/ James E Watson INVENTOR BY \XM 23. m

ATTORN EY Nov. 5, 1968 J. F. ,WATSON 3,409,483

SELECTIVE DEPOSITION OF SEMICONDUCTOR MATERIALS v I Original Filed May 1, 1964 2 Sheets-Sheet 2 20 I 3o \Y\\\\I Fig.5

' James F. Watson 8 Y Y INVENTOR ATTORNEY w J 13,409,483. SELECTIVE DEPOSITION-.- OF

- A E L James F. Watson, R i cha1-dson, Tex., assignor toTexas Instrumentslncorporate'd, Dallas, Tex a corporation of .Delaware semcosbmlok;

Continuation of application SernNof 364,23'4,'*M'ay 1',

' 1964. This application May 26, 1967, Set. No.'-641,704

- 7Claims.(Cl.148-175) f t ABS TRACT OF THE DISCLO S IIRE A method or depositing small: [limited areaepitaxial regions on a body of semiconductor material. A masking layer such a.s ,silicon oxide orv magnesium fluoride;is used to define a pattern of openings where epitaxial material is a to be grown, followed by said epitaxial. growth. The-masking layer may be removed and the process repeated-to create a complex structure without disturbing shallow underlying layers. Specific cornbinationsof steps to obtain specific complex structures are claimed. The application of the process to the fabrication of integrated circuits is disclosed.

3,409,483 Ratented Nov. 5, 1968 the mask may be used "to create a complex structure without disturbing shallow underlying layers :Thernovelfeatures believed-characteristic of this invention' are set forth 'imthe appended claims. The--invention itself, as well as other objects and advantages thereof, will best'be'understood, however, by reference-tothe following description of illustrative embodiments, when read in conjunction with the accompanying drawings, wherein: FIGURE 1 is a front elevation, partly in section, of one form of apparatusused' for the growth of epitaxial films; FIGURES -2 through 5 are elevation views in section of adevice made accordingto this invention-at various stages This application is a continuation of application Ser.

With a high degree of 'depth control, conductivity,and

lateral extent of the regions. Diffusion techniques using oxide masking, such as illustrated in thepatent to Andrus 3,112,817, offer excellent geometrical control and have gained wide acceptance. However, diffusion of impurities does not permit complete control of the impurity concentration, in that the distribution will always follow a certain gradient so that a second'or third diffusion must always be of higher concentration than the previous'one if the conductivity-type is to be converted.For'this reason, epitaxial deposition has been employed in the semiconductor arts to produce surface layers of uniform and controlled impurity concentration. Typically, a transistor or integrated circuit is made by growing an epitaxial layer over an entire face of a semiconductor wafer or'slice, and then limiting the active or effective area of the epitaxial layer by mesa etching or isolation diffusion. In some cases, however, especially if multiple thin layers are .involved, these two techniques are unsuitable since the depth of the operation cannot be accurately controlled.

. It is therefore the principal object of this invention to i provide a method of depositing small, limited-area epitaxial regions on a body of semiconductor material. Another object is to provide improved semiconductor devices of the type including epitaxial layers. A further object is to provide a method of masking the deposition of semi conductor materials.

In accordance with this invention, a masking layer is grown or deposited onto a semiconductor surface prior to the epitaxial. deposition. This layer is composed of a material, such as silicon oxide, which adheres to the semiconductor surface but to which the subsequently grown seminconductor material willnot adhere. Themasking layer may define a pattern of openings where epitaxial material is to be grown. A succession of repetitions of the steps of masking, epitaxial growth, and removal of of manufacture; and; I a -FIGURES 6 through 8'are elevation views in section of another embodiment at various stages in manufacture; As the-term, is used in semiconductor technology,

. epitaxial deposition involves the addition of semiconductor material to a crystalline substrate in such-a manner that the crystallographic orientation and-periodicity is maintained. As ordinarily practiced, the technique involves a pyrolytic or a pyr-olytic-disproportionation type of chemical reaction, generally involving a halogen transport element wherein semiconductor material in the form of a halide compound is caused to decompose on a semiconductor crystal, substrate to provide a deposit which retains the orientation and periodicity of the crystalline-substrate. Most common perhaps is the deposition of an epitaxial silicon film on a silicon substrate by the hydrogen reduction of silicon tetrachloride. The substrate usually has an interatomic spacing very close to that of the deposited material, and may be of the same or a different semiconductor material. The conductivity type and impurity con centration of the deposited material are controlled'byentraining the appropriate materials in the gaseous stream which passes over the substrate. In thismanner, N-type silicon may be deposited onto P-type silicon, or. onto N- type silicon of a different conductivity, for example, or germanium. may be grown upon gallium arsenide. Techniques for epitaxial deposition are illustrated in US. Patents 2,692,839, 2,763,581, 3,089,794, and French Patent 1,282,020. t

Referring now to FIGURE 1, apparatus for growing epitaxial films as employed in this invention may comprise an epitaxial reactor in the form of a tube furnace 10 having a heating coil 11. A boat 12 holding several silicon slices 13 is disposed within the tube furnace in such a position as to expose the slices to gases directed into the tube from a conduit 14. Purified dried hydrogen enters an end 15 of the conduit. Silicon tetrachloride vapor is introduced into the conduit from a flask 16 -of liquid silicon tetrachloride submerged in a reservoir 17 of liquid nitrogen. The vapor pressure of silicon tetrachloride is regulated by the degree of refrigeration of the flask 16 in which the hydrogen gas is saturated. The flow of gases into the tube furnace is regulated by conventional valves. Doping impurities may be introduced into the gas stream by placing the appropriate impuritycontaining compound, such as a halide of boron or phosphorus, into the flask 16 or in a similar flask if a different temperature is needed. With the arrangement of FIGURE 1, silicon is deposited upon the slices 13, and grows epitaxially, due to hydrogen reduction of silicon tetrachloride. Of course, other. materials and other deposition techniques are equally applicable to this invention.

In practicing this invention, the slices 13 in FIGURE 1 would contain a masking pattern to produce the desired epitaxial growth. With reference to FIGURE 2, a wafer 20 of 'monocrystalline silicon is shown which has a thermally grown silicon oxide'coating 21. An opening 22 corresponding to the shape of the desired epitaxial ragion, is cut in the silicon oxide by photoresist masking and etching in accordance with standard practice. This wafer slice of perhaps one inch diameter which would contain dozens or hundreds of likeelements. The wafer as seen in;FIGURE 2, being. part ofaslice,:is placed'in the reaction chamber of'FlGURE l where silicon deposits adhere to theexposed silicon surface in theopenin'g- 22 but'n'otto the. oxide 21.-.A limited-area layer 23 may thus be grown; as seen in FIGURE 3,.andthis layer may beiof opposite type conductivity than-the'substrate'; i.e.-, P-type on N-type-.;-It*is, noted. that the edge .of the p-n junctionbetweentheregion 23-.and the substrat'e'20 is completely enclosed-within the'silicor'r oxide, passivating and'stabilizing the device. Thereafter; another'oxide coaring-24 as seemin FIGURE -4rnay be grownI'on thetop surface of the:- wafer over the layer 23 and an opening 25 cut. The slice is placed in the reactor=again and an N-typeregion-26' gro'wn thereon. Itis seen here that the small region-26 is provided without the'necessity of disturbi-ngflthe underlying layer 23 with mesaetchin'g or 'isolation ditfusions. Also, very small'geometries,measured in.=mils'or:tenths of mils, may be obtained by='the photo'- graphic methods used to define the holes'in the oxide; The device'of. FIGURE 4; an NPN transistor, is completed 'by growing another oxide layer 27, see FIGURE 5, openingholes for contacts, then depositing metal for the emitter'and base contacts 28 and 29, which may be expanded out over the oxide layer as shown. A collector a another layer t'oforin said device;

contact 30 is appliedto the back of the wafer. The rela- 3 tive thicknesses of the various layers of different materials are not necessarily to-scale, the oxide actually being much thinner than the epitaxial layers;

In integrated circuits, where many circuit components may be formed within a monocrystalline 'body, this invention has great utility because of the great flexibility permitted in determining the conductivity-type, resistance, and even the type of material, in a complex multilevel structure. With reference to FIGURE 6, a Wafer 32 has a circuit component such as a diode 33 formed in one face thereof. The techniques of this invention are used to grow arr epitaxial P-lregion 34 which is masked by an oxide layer 35. The oxide is removed and the layer 34 masked by oxide layer 36 as seen in FIGURE 7. Then high resistivity semiconductor material is epitaxially grown on the peripheral area of the wafer face to provide an intrinsic barrier region 37. This may be composed of intrinsic-appearing, chromium-doped gallium arsenide, for example, whereas the region 34 could be highly conductive germaniurn. Thereafter, a layer 38 bf epitaxial semiconductor could be grown across the entire top of the wafer, thcna circuit component such as a transistor -39'formed in the layer. It is seen that the collector of the transistor 39 is connected to the anode of the diode 33 by the completely enclosed region 34 whereas all other portions of the layer 38 are insulated from the substrate 32. Of course, the various layers could have many circuit components therein, and the layers could be built up to produce an extremely complex cir- 1. A method of manufacturing a semiconductor device, comprising the steps of forming a first masking layer on and adhered to a surface of a semiconductor body, removing a portion of saidffir's't rnasking IQYQ T tqforrn an opening exposing-"alimit edarea said surface, epitaxial ly depositing afirst semicbnduc'torlayer upon said surfi in's' id b fi,. r o ;ihe ma ing ay r, 'fQ iriganoth er 'fnaski'ng' layefov'er' said first epitaxial depositedsemiconductor. layer depositing. a second epitaxial layer of.,high resistivity material, around. said: firstgepitaxial layer, and? forming afsemiconductor device upon said second layer. H H" 2. The method according to'claifit'r wherein said semiconductor device for-med upon said second semiconductor layer is formed by depositing another epitaxial layer over said' 's econd layer and diffusing impurity rn'aterialinto said S'. The methodaccordingto claim1"wherein said first masking'layer is'silicon monoxide. 3 i f 45 The methodiaccording to claim 1' wherein said first masking layer is magnesium-fluoride. 5. The method according to claim 1 wherein said high resistivity epitaxial layer is composed of intrinsic appearing chromium doped gallium arsenide.

6. The method according to claim 1 wherein said surface of said body below said opening is P-type constituting one region of a diode and said first epitaxial layer interconnects said diode with said semiconductor device.

7. A method of manufacturing multi-layer semiconductor'devices, comprising the steps of diffusing at least one region in a semiconductor substrate to form at least one' semiconductor device, masking the surface of said substrate, removing a portion of said'mask to expose a region-of said semiconductor device, epitaxially depositing semiconductor material on the exposed region, removingsaid masking material,fmasking said epitaxial deposited material, epitaxially depositing high resistivity in sulatingmaterial over unmasked portions of 'said substrate, removing the masking material from said epitaxialdeposited material, epitaxially depositing'a layer of semiconductor material over said first epitaxial deposited-material and said high resistivity insulating ma-v cuit wherein all interconnections are enclosed within the monocrystalline semiconductor block.

Instead of using silicon dioxide as the masking material as set forth above, other dielectrics such as silicon monoxide or magnesium fluoride could be used. These two materialscanboth be applied by evaporating and condensing onto a hot substrate, about 350 C. for silicon.

While this invention has been described with reference 'to specific embodiments, this description is not to be construed in a limiting sense. Various modifications of ,the disclosed embodiments, as well as other embodiments of the invention, will now be apparent to persons skilled in the art, and so it is contemplated that the appended claims will cover any such modifications, or embodiments as fall within the true scope of the invention.

terial, and forming at least one semiconductor device in said epitaxial layer covering said insulating layer, said 'first deposited epitaxial material interconnecting said at ,least one semiconductor device in said substrate and at leastone device formed in said epitaxially deposited layer of semiconductor material.

. References Cited UNITED STATES PATENTS 2,780,569 2/1957 Hewlett 148- 174 2,983,631 5/1961 Hanlet 148-174 3,025,589 3/1962 Hoerni 148-175 3,098,774 7/1963 Mark 148-175 3,140,965 7/1964 Reuschel 148-175 3,156,591 10/1964 Hale et a] 148-175 3,189,973 6/1965 Edwards .et al. 117-201 3,206,339 9/1965 Thornton 148-175 3,234,058 2/1966 Marinace 148-175 3,265,542 1 8/1966 Hirshon 148-175 3,296,040 1/1967 Wigton 148-175 OTHER REFERENCES Armed Services Technical Information Agency, Report No; AD 282; 249, p. 30, Aug. 17,1962. Allen et al.: Metallurgy of Semiconductor Material, vol; 15, pp. 113-115,;Aug. SO-Sept. 1,,1961.

L. DEWAYNE RUTLEDGE, Primary Examiner. P. WEIN STEIN, Assistant Examiner. 

